Lubricant inhibitor

ABSTRACT

A GREASE INHIBITED AGAINST OXIDATION AND AGAINST INHIBITOR RECRYSTALLIZATION CONTAINING A LUBRICANT GELLED TO GREASE CONSISTENCY, AN AMOUNT OF A PHENOTHIAZINE-TYPE INHIBITOR SUFFICIENT TO INHIBIT OXIDATION, AND A PYRROLIDONE COMPOUND THAT IS LIQUID PHASE AND IN AN AMOUNT SUFFICENT TO PREVENT LARGE CRYSTALS OF PHENOTHIAZINE-TYPE INHIBITOR FROM FORMING. TYPICALLY THE GREASE WILL CONTAIN UP TO ONE PERCENT BY WEIGHT BY PHENOTHIAZINE AND ABOUT THE SAME AMOUNT OF N-METHYL PYRROLIDONE.

United States Patent 3,629,108 LUBRICANT INHIBITOR Gerard P. Caruso, New Orleans, La., assignor to Shell Oil Company, New York, N.Y. No Drawing. Filed Sept. 12, 1968, Ser. No. 759,519 Int. Cl. Cm 3/32, 7/36 US. Cl. 252-28 11 Claims ABSTRACT OF THE DISCLOSURE A grease inhibited against oxidation and against inhibitor recrystallization containing a lubricant gelled to grease consistency, an amount of a phenothiazine-type inhibitor sufficient to inhibit oxidation, and a pyrrolidone compound that is liquid phase and in an amount sufficient to prevent large crystals of phenothiazine-type inhibitor from forming. Typically the grease will contain up to one percent by weight of phenothiazine and about the same amount of N-methyl pyrrolidone.

BACKGROUND Lubricants in general and greases in particular are improved by including small amounts of oxidation inhibitor within their compositions. Very favorable oxidation inhibitors are those of the phenothiazine type, e.g., phenothiazine, 3,7-dialkyl phenothiazine and N-substituted derivatives. Althought phenothiazine-type inhibitors are very successful in reducing oxidation effects in the lubricant, they are insoluble in lubricating oils and are in solid form at room temperature. For most applications, the phenothiazine inhibitor can be added as extremely small crystals so that the lubricating quality of the composition is not impaired; but when high temperatures are encountered in the lubricating environment, the phenothiazine-type inhibitor melts or dissolves and upon subsequent cooling of the lubricant, large macroscopic crystals of the inhibitor are formed giving a non-homogeneous product. These large crystals detract greatly from the value of the lubricant from the viewpoint of its appearance as a uniform product and the fact that the crystals are capable of being removed from the grease if it is pumped through screens or filters before being placed in ball or roller bearings.

THE INVENTION This invention involves an additive for lubricating compositions which eifectively inhibits oxidation and avoids the problem of recrystallization of inhibitors. The additive of this invention is a solution of a phenothiazine-type inhibitor in a pyrrolidone compound that is in liquid phase. The liquid phase of the pyrrolidone compound is evaluated against the anticipated conditions of use. For example, for ordinary uses a pyrrolidone compound that is liquid phase at room temperature is adequate; but if extremely low temperature uses are anticipated, the pyrrolidone compound should be liquid phase at the low temperatures anticipated for use and for storage.

The invention also involves a lubricating composition consisting of a lubricating liquid having distributed therein an amount of phenothiazine inhibitor effective to inhibit oxdation, and an amount of liquid phase pyrrolidone compound etfective to reduce crystal formation of the phenothiazine inhibitor.

In accordance with this invention, it has been found that phenothiazine-type inhibitors are soluble in liquid phase pyrrolidone compounds and that the inhibitor may be added to lubricants in the form of the solution. It is also within the scope of this invention to add the phenothiazine-type inhibitor and the pyrrolidone compounds sepa rately to the lubricant so that the solutions may be formed in situ. Although this invention should not be limited by the following explanation, it is presently thought that the inhibiting elfect of the pyrrolidone compound is a property of the solubility of phenothiazine in the pyrrolidone compound. Apparently, the pyrrolidone compound is also not soluble in ordinary lubricating oils; and it is, after a period of use, uniformly distributed throughout the lubricating oil in the form of very small droplets of liquid. These droplets of liquid have a selective dissolving action for the phenothiazine-type inhibitor although they do not diminish the qualities of the inhibitor for preventing oxidation. It is thought that upon use at high temperature the phenothiazine either liquifies or dissolves in the oil and there is no problem of crystallization; however, when use at high temperatures stops and the temperature of the lubricating medium is reduced, the phenothiazine inhibitor enters the pyrrolidone compound and remains either in liquid phase dissolved in the pyrrolidone compound or in the form of very small crystals which are limited in size by the size of the surounding liquid pyrrolidone compound. Since the pyrrolidone compound is insoluble in the oil phase, each droplet of liquid pyrrolidone compound is separate from each other droplet and coalescing is avoided by the surrounding lubricant. Additionally, since phenothiazine inhibitors are soluble in pyrrolidone compound, the size of crystals is limited because most of the phenothiazine is in solution and therefore not available for crystal formation.

The presence of any pyrrolidone compound in the phenothiazine-inhibited lubricating composition will, of course, mitigate the recrystallization problem. However, it has been found that equal weights of inhibitor and pyrrolidone compound substantially obviate the recrystallization problem. The crystallization in most compositions can be avoided when the weight ratio of pyrrolidone to phenothiazine is about 0.5; and when the weight ratio of pyrrolidone to phenothiazine is 2.0, there is substantially complete solubility of phenothiazine in pyrrolidone and no crystal formation under any circumstances should be expected. Accordingly, it is preferred that the weight ratio of pyrrolidone compound to phenothiazine-type inhibitor should be from about 0.5 to about 2.0, both in an inhibiting comopsition before it is added to the lubricating composition and in the lubricating composition.

As with most inhibitors, only small quantities are required to produce a dramatic effect in improving a lubricating composition. Thus, phenothiazine-type inhibitors present in a lubricating compisition in as small an amount as 0.25 percent produce noticeable improvement in the oxidation characteristics of the lubricant. It is preferred that from about 0.5 to about 1.0 percent phenothiazine compound be present in the lubricant and that the pyrrolidone compound should be present in the weight ratio to phenothiazine mentioned above.

Phenothiazine-type inhibitors are known to the art and many different types have been found to be effective. Within the scope of this invention, it has been found that phenothiazine, 3,71diisooctyl phenothiazine, N-benzyl-B, 7-dioctyl phenothiazine, among others, are especially useful. Also, as described above, pyrrolidone compounds which are liquid phase at the anticipated temperature of storage or the ambient temperature where used, may be used. Particularly useful pyrrolidone compounds are N-methyl pyrrolidone and 2-pyrrolidone, among others.

Other conventional additives such as extreme pressure agents, anti-wear agents, corrosion inhibitors, and the like may also be present in the lubricants of this invention without departing from hte scope thereof.

Following are a group of examples presented to illustrate various embodiments of this invention. In all examples, a grease was prepared employing either a lithium soap or a waterproofed montmorillonite clay as the gelling agent. Each of the compositions reported in the table that follows was prepared by adding inhibitor to the grease, thoroughly mixing the grease and inhibitor and then heating the mixture to a temperature between 210 and 220 C, for a time sufficient to cause all inhibitor to enter the liquid phase. The inhibitor employed was either the oxidation inhibitor by itself or a solution of the oxidation inhibitor in the crystallization inhibitor. After preparation, the grease was cooled to room temperature and stored at room temperature. The grease structures were microscopically examined periodically to determine the extent and character of crystal formation within the grease. The results of these observations are recorded in the following table.

rystal formation .iitcr After 1 day .5 nmiths Oxidation Crystal inhibitor llillihlit)! Grease Number None LTEiI. Your.

\oiie Large"... Very large.

. None Large.

NOTE: C =Piieuothiazine; phenothiazine; I? N-methyl pyrrolidone; u 'Z-pyrrolidone.

A Lithium soap; B=Wuterpro0fed montmorillonite clay;

l)=l)iis0octyl phenothiazine; E Benzyldiouty The data presented in the table indicate that the inhibitor mixture of this invention is effective to inhibit crystal formation of phenothiazine-type inhibitors in grease. In almost every test, crystal formation was prevented completely. In those cases where crystals formed in the grease that was inhibited in accordance with this invention, the crystals were much smaller in size than those formed in greases without crystal inhibition, and they formed only after a prolonged period of time.

The pyrrolidone compounds useful in this invention are those that dissolve phenothiazine-type inhibitors and are liquid at the conditions of use. Pyrrolidone compounds that are substituted on either nitrogen or carbon atoms may be used, and substituents may be alkyl or automatic or both provided the pyrrolidone compounds produce the functions noted above.

I claim as my invention:

1. An additive for lubricating compositions consisting essentially of (1) a phenothiazine oxidation inhibitor which is substantially insoluble in the lubricating medium in which it is employed dissolved in [2) a pyrrolidone compound which is in liquid phase and is also substantialaios 1y insoluble in the lubricating medium in which it is employed,

2. The composition of claim 1 wherein said pyrrolidone compound is N-methyl pyrrolidone.

3. The composition of claim 1 wherein said pyrrolidone compound is 2-pyrrolidone.

4. The composition of claim 1 wherein said inhibitor is phenothiazine.

5. The composition of claim 1 wherein said inhibtior is phenothiazine and said pyrrolidone compound is N- methyl pyrrolidone.

6. The composition of claim 1 wherein the weight ratio of pyrrolidone compound to phenothiazine inhibitor is from about 0.5 to about 2.0.

7. A lubricating composition consisting essentially of (A) a lubricating liquid gelled to grease consistency (B) sui'ficient phenothiazine inhibitor to inhibit oxidation, said phenothiazine inhibitor benig substantially insoluble in said lubricating liquid (C) suflicient liquid phase pyrrolidone compound to inhibit crystal growth of said phenothiazine inhibitor, said pyrrolidone compound also being substantially insoluble in said lubricating liquid.

8. The composition of claim 7 containing up to one percent phenothiazine, 3,7-diisooctyl phenothiazine or N- benzyl-3,7-dioctyl phenothiazine and up to 2 percent N- methyl pyrrolidone or 2-pyrrolidone.

9. The composition of claim 7 wherein the weight ratio of pyrrolidone compound to phenothiazine inhibitor is from about 0.5 to about 2.0.

10. The composition of claim 7 wherein said lubricating liquid is gelled with lithium soap.

11. The composition of claim 7 wherein said lubricating liquid is gelled with waterproofed montmorillonite clay.

References Cited UNITED STATES PATENTS 2,781,318 Z/l957 Cyphers 25247 3.078.230 2/1963 Cyba 25247.5 3,179,590 4/1965 Loefiier et a1. 25228 FOREIGN PATENTS 1,321,009 2/1963 France 252--47.5

DANIEL E. WYMAN, Primary Examiner I. VAUGHN, Assistant Examiner US. Cl. X.R. 

